Broadcasting is becoming increasingly digital in all countries, but in a receiver that receives a digital broadcast, in order to receive the digital broadcast, it is necessary to execute a channel scan in a pre-assigned digital broadcast frequency band.
As a technique for shortening the time needed for channel scanning in a receiver that receives a digital broadcast, there is the technique described in Patent Reference 1. Patent Reference 1 describes a receiver with a plurality of front ends (tuners and demodulators); in order to complete a channel scan quickly, the frequency band in which the channel scan is to be performed is divided into subbands, and the front ends perform channel scans of the subbands in parallel.
In China, digital broadcasting is carried out by DTMB (Digital Terrestrial Multimedia Broadcast), which provides high-definition programs to fixed receivers, and by CMMB (China Multimedia Mobile Broadcasting) for mobile devices.
In Japan, 12-segment broadcasting to fixed receivers and 1-segment broadcasting to mobile devices are carried out by the ISDB-T (Integrated Services Digital Broadcasting-Terrestrial) system. In ISDB-T, the 12-segment and 1-segment broadcasts are both multiplexed into a signal physical channel. The 12-segment and 1-segment broadcasts can both be received with a single demodulator chip, because the demodulation system is the same for both in ISDB-T.
China's DTMB and CMMB are similar to the 12-segment and 1-segment broadcasts of ISDB-T in that they broadcast to fixed receivers and mobile receivers, but the DTMB and CMMB broadcast protocols and demodulation systems differ. Separate demodulator chips are therefore required for DTMB and CMMB. In addition, the demodulated DTMB stream is in the TS format but the demodulated CMMB stream is in the MF (Multiple Frame) format, so the filtering processes that extract compressed audio data and compressed video data from these streams differ between the two, and the broadcast wave information on the basis of which service lists are generated also differs.
The DTMB and CMMB digital broadcast systems share the same frequency band. DTMB is broadcast on physical channels 13 to 56; CMMB is broadcast on physical channels 13 to 48. The DTMB and CMMB center frequencies corresponding to the same physical channel number are identical. On physical channels identified by the same physical channel number, accordingly, either DTMB or CMMB is broadcast but not both.
First a brief description of DTMB will be given. Within a physical channel there is one TS, in which network and service broadcast wave information, program information, and so on are multiplexed in addition to the actual audio and video service data. PSI and SI are used in DTMB, and the compressed audio and video stream separation methods, the PSI and SI extraction methods, and so on are extremely close to those of the ISDB-T and DVB-T systems. The service list is therefore generated from information extracted in a PSI and SI channel scan, as in ISDB-T.
Next a brief description of CMMB will be given. A plurality of MFs are multiplexed within a physical channel, and the network and service broadcast wave information, program information, and so on differ from the DTMB system. The broadcast wave information is defined as a CIT (Control Information Table) and transmitted in its own MF. In the CIT, the network identifier, network name, transmission frequency, and so on are transmitted in a NIT (Network Information Table). Information relating services to MFs is included in a MCT (Multiple Configuration Table) in the CIT. The receiver extracts the CIT in a channel scan and generates a service list.
The DTMB and CMMB systems thus differ in regard to both front end processing in the tuner and demodulator and back end processing in which demultiplexing and decoding are performed, so it is necessary to provide a separate receiver for receiving each system.
If a receiver is configured to receive both the DTMB and CMMB systems, since the demodulator and demultiplexer for DTMB reception differ systematically from the demodulator and demultiplexer for DTMB reception, they are generally configured separately.
A channel scan must be carried out for the receiver to preset the broadcast services broadcast throughout the band; when a channel scan is carried out with the above general configuration, a DTMB mode and a CMMB mode are provided and the receiver carries out a channel scan of the broadcast protocol corresponding to each mode.
In this regard, since the receiver described in Patent Reference 1 is designed for a single broadcast protocol, when the receiver described in Patent Reference 1 carries out a channel scan of DTMB and CMMB broadcasts, if the DTMB broadcasts are processed by two front ends designed for the DTMB system, the time required for the DTMB channel scan can be reduced to half the time for a channel scan of the entire band with one front end. If the CMMB broadcasts are processed by two front ends designed for the CMMB system, the time required for the CMMB channel scan can also be reduced to half the time for a channel scan of the entire band with one front end.